Cement mixtures with alkali-intolerant matter and method

A method of reinforcing cement/concrete mixtures with alkali-intolerant reinforcements and/or aggregate, such as uncoated, common glass filament, plastic filament, fabric and roving made therefrom by reducing the pH of the mixture while in its plastic state, and/or after it has set and cured, to about 7. With a neutral pH, the alkali-intolerant reinforcements need not be coated to protect them from degradation. In the absence of alkalinity, the reinforcement and/or aggregate material bonds with the cement mixture to form a relatively stronger mixture, which can be shaped as desired, made part of permanently poured structures, cement boards and many other small and large products. By selecting appropriate and, if desired, different materials for the reinforcements and/or aggregate, the strength, flexibility, etc. characteristics of the product can be readily changed to adapt the product to the intended use. The pH is reduced by migrating such materials as CO.sub.2 and/or CO and O.sub.3 into the cement after it has cured and, if desirable, also during curing. The CO.sub.2 and/or CO and O.sub.3 for the chemical reactions to reduce the pH are most suitably obtained from flue gases of independent combustion processes which would otherwise be discharged as atmospheric pollutants.

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Claims

1. A method of protecting alkali-intolerant material in a cured cement product comprising the steps of mixing dry cement, ground calcite, and an alkali-sensitive material, adding water to form a paste, molding the paste into a product, curing the product, exposing the cured product to carbon dioxide, and reducing the pH of the mixture to about 7 by generating calcium carbonate in calcite form.

2. A method according to claim 1 wherein the step of reducing the pH is at least in part performed after the step of curing has been substantially completed.

3. A method according to claim 2, wherein the step of reducing the pH is partially performed before the mixture has fully cured.

4. A method according to claim 1, wherein the step of reducing the pH is accomplished by adding CO.sub.2.

5. A method according to claim 4, wherein the step of adding CO.sub.2 is performed before the mixture has set.

6. A method according to claim 5, wherein the step of adding CO.sub.2 comprises entraining CO.sub.2 gas in the mixture.

7. A method according to claim 6, wherein the step of adding CO.sub.2 comprises the step of injecting a foaming agent into the mixture, and foaming the foaming agent with a gas including CO.sub.2 gas.

8. A method according to claim 7, including the step of varying the proportion of CO.sub.2 gas in the foaming gas.

9. A method according to claim 4, wherein the step of adding CO.sub.2 comprises the step of adding the CO.sub.2 to the mixture after the mixture has set.

10. A method according to claim 9, wherein the step of adding CO.sub.2 comprises the steps of immersing the mixture, after it has set, in a bath of carbonated water.

11. A method according to claim 1 wherein the step of reducing comprises adding to the mixture at least one material selected from the group consisting of CO and CO.sub.2.

12. A method according to claim 4, wherein the step of adding CO.sub.2 comprises placing the mixture in an atmosphere including CO.sub.2 gas.

13. A method according to claim 12, including the step of raising the pressure of the atmosphere to above ambient pressure.

14. A method according to claim 13, wherein the atmosphere comprises predominantly CO.sub.2 gas.

15. A method according to claim 14, including the step of cooling the mixture while adding the CO.sub.2 gas.

16. A method according to claim 15, including the step of cooling the mixture to a temperature in the range of between about 0.degree. C. and 10.degree. C.

17. A method according to claim 16, wherein the step of cooling comprises the step of maintaining the mixture at a temperature above 0.degree. C.

18. A method according to claim 4 wherein the CO.sub.2 utilized is produced by reacting carbon monoxide and ozone to form carbon dioxide and oxygen.

19. A method according to claim 14 including the step of removing the oxygen produced during the reaction of carbon monoxide and ozone prior to the step of adding CO.sub.2.

20. A method according to claim 1 wherein the step of reducing the pH is accomplished by reacting carbon monoxide with the mixture to form calcium carbonate and hydrogen.

21. A method according to claim 20 wherein the hydrogen reacts with ozone to produce water, oxygen, and thermal energy.

22. A method according to claim 18 including the step of separating the oxygen produced during the reaction of carbon monoxide and ozone.

23. A method according to claim 22 wherein the step of separating the oxygen further includes the step of utilizing the oxygen in a combustion process.

24. A method according to claim 20 wherein the flue gas from a combustion process is used as a source of carbon monoxide.

25. A method according to claim 24 wherein the source of ozone is from a combustion process.

26. A method of reinforcing cured cement mixtures with a material having alkali-intolerant or alkali-sensitive exterior surfaces comprising the steps of mixing at least cement, water, calcite and the material to form a paste, shaping the paste into a product, curing the product, exposing the cured product to carbon dioxide or carbon monoxide drying the product, and continuing the carbon dioxide exposing step until substantially all calcium hydroxide has reacted into calcite and the pH of the product is about 7.

27. A method according to claim 26, wherein the alkali sensitive material is a fiberglass filament.

28. A method according to claim 26 wherein the alkali sensitive material is a aggregate.

29. A method according to claim 26 wherein the material comprises at least one of fibers and aggregate at least some of which are made from different materials.

30. A method according to claim 26 wherein the step of exposing is performed after the product is fully cured.

31. A method according to claim 26 wherein the step of exposing comprises adding only CO.sub.2 to the mixture.

32. A method according to claim 31 wherein the step of exposing is at least partially performed when calcium hydroxide is being formed to thereby reduce the pH of the mixture during curing to about 7.

33. A method of providing cured cement mixtures with material having alkali-intolerant exterior surfaces comprising the steps of mixing dry cement powder, ground calcite, and an alkali-sensitive material, adding water to form a paste, shaping the paste into a product, curing the product, exposing the product to a carbon dioxide atmosphere, and drying and repeating the carbon dioxide exposing step until substantially all calcium hydroxide has reacted into calcite and the pH of the product is reduced to about 7 as a result of converting calcium hydroxide which is present in the product into calcite.

34. A method according to claim 33 wherein the step of exposing includes the step of placing the product in a gas atmosphere of CO.

35. A method according to claim 33 including the step of pressurizing the atmosphere to above atmospheric pressure.

36. A method according to claim 35 including the step of cooling the product during the step of exposing it to the gas atmosphere.

37. A method according to claim 36 wherein the cooling step includes maintaining the product temperature in the range of between about 0.degree. and 10.degree. C.

38. A method according to claim 37 wherein the temperature is about 2.degree. C.

39. A method according to claim 30 wherein the step of exposing comprises immersing the product in a bath including CO.sub.2.

40. A method according to claim 33 wherein the step of exposing includes reacting the at least one of carbon dioxide and carbon monoxide with calcium hydroxides in the product to generate calcite.

41. A method according to claim 33 including the step of increasing a porosity of the product by foaming.

42. A method according to claim 41 wherein the step of increasing the porosity comprises the step of adding a foaming agent to the slurry.

43. A method according to claim 42 wherein the foam material is an aqueous foam.

44. A method of reinforcing cured cement mixtures with fibers having alkali-intolerant exterior fiber surfaces comprising the steps of mixing dry cement powder, ground calcite, and alkali-sensitive fibers and adding water to form a paste therewith, shaping the paste into a product, curing the product, exposing the cured product to carbon dioxide, drying and repeating the carbon dioxide exposing step until substantially all calcium hydroxide has reacted into calcite, the stable form of calcium carbonate, and reducing the pH of the product to about 7.

45. A method according to claim 44 wherein the step of combining and mixing includes adding fibers made of different materials.

46. A method of protecting alkali-intolerant material in a cured cement product against degradation of the material by calcium hydroxide comprising the steps of mixing dry cement powder, ground calcite, and alkali-sensitive materials and adding water to form a paste therewith, shaping the paste into a product, curing the product, exposing the cured product to a carbon dioxide atmosphere by using flue gases from a combustion process of at least one of CO and CO.sub.2 and mixtures thereof, reacting at least one of CO and CO.sub.2 with calcium hydroxide in the product to form calcium carbonate as substantially calcite in an amount sufficient to reduce the pH of the mixture to about 7, and continuing the exposing step until substantially all calcium hydroxide has reacted into calcite.

47. A method according to claim 46 wherein the step of exposing is at least partially performed after the product has fully cured.

48. A method according to claim 46 wherein the step of exposing includes the step of generating heat.

49. A method according to claim 46 wherein the step of exposing includes cooling the temperature of the product to no more than about 10.degree. C.

50. A cured cement product comprising at least cement, a filler, and material distributed throughout the product which has alkali-intolerant exterior surfaces in contact with a remainder of the product, the product including calcium carbonate in the form of substantially calcite, having a pH of about 7 and made by mixing dry cement powder, ground calcite, and an alkali-sensitive material and adding water to form a paste therewith, shaping the paste into the product, curing the product, and exposing the cured product to carbon dioxide until substantially all calcium hydroxide has reacted into calcite.

51. A product according to claim 50, wherein the alkali sensitive material is uncoated fibers.

52. A product according to claim 51, wherein the fibers are glass.

53. A product according to claim 51, wherein the fibers are plastic fibers.

54. A product according to claim 50, wherein the material is an uncoated aggregate made of alkali-intolerant material.

55. A product according to claim 50, wherein the alkali sensitive material is a a cloth.

56. A product according to claim 50, wherein the alkali sensitive material is a roving.

57. A product according to claim 50, wherein the alkali sensitive material is glass fibers, and wherein the product is a glass fiber reinforced cement board.

58. A cured cement product comprising at least cement including calcium carbonate in the form of calcite and at least one of fibers and aggregate distributed throughout the product and having alkali-intolerant exterior surfaces in contact with a remainder of the product, some of the at least one of the fibers and the aggregate being made from a different material than others of the at least one of the fibers and the aggregate, the product being made by mixing dry cement powder, ground calcite, and an alkali-sensitive material and adding water to form a paste therewith, shaping the paste into the product, curing the product, and exposing the cured product to carbon dioxide until substantially all calcium hydroxide has reacted into calcite and having a pH about 7.

Referenced Cited
U.S. Patent Documents
4069063 January 17, 1978 Ball
5043020 August 27, 1991 Lerke et al.
5307876 May 3, 1994 Cavan
5358676 October 25, 1994 Jennings et al.
Foreign Patent Documents
0181261 May 1986 EPX
2409217 September 1975 DEX
3017631 February 1978 JPX
3094516 August 1978 JPX
7071847 May 1982 JPX
9000564 January 1990 KRX
Other references
  • Concrete Technology and Practice Taylor (1965) pp. 439-441. Japan Patent Abstract--"Production of High Strength Cured Cement Material Utilizing Carbonation Reaction" Suzuki et al. JP 06-263562 (Sep. 20, 1994). Japan Patent Abstract "Production of High Oil Resistant Cement Hardened Body" Suzuki et al. JP 06-10749 (Apr. 19, 1994). Japan Patent Abstract "Mineral Aggregate Resistant to Reacton with Base & Method for Suppressing Base-Aggregate Reacton" Tsuyuki et al. JP 04-74740 (Mar. 10, 1992). "Environmental Protection for Concrete", Stanfield Pigment & Resin Technology (United Kingdom) (1987) 16, (10) 8-13 See Abstract. "Study of the Endogeneous Carbonation of Concrete and of its Application to the Precast Concrete Industry" Estoup et al. Thesis--Univ. of Paris (1987)--See Abstract--. "Plasma Treated Ultra High Strength Polyethylene Fibers Improved Fracture Toughness of Polymethymethacrafatic" Hild et al. J. of Mat'ls Science V4 N5 (1993). Cement and Concrete Research, Perez-Pena, M., et al. (1994), "Mechanical Properties of Fiber Reinforced Lightweight Concrete Composites", pp. 1121-1132. Cement and Concrete Research, Wang, Shao-Dong, et al. (1994), "Factors Affecting the Strength of Alkali-Activated Slag", pp. 1033-1043. Magazine of Concrete Research, Loo, Y.H., et al. (1994), "A carbonation prediction model for accelerated carbonation testing of concrete", pp. 191-200. American Concrete Institute, Bentur, A. (1990), "Improvement of the Durability of GFRC by Silica Fume Treatments", pp. 215-222, 225-231. American Concrete Institute (1989), "Cold Weather Concreting", pp. 306R-1, 4, 19. Concrete Technology and Design, Swamy, R.N. (1988), "Natural Fibre Reinforced Cement and Concrete", pp. 170-172. Prestressed Concrete Institute (1987), "Recommended Practice for Glass Fiber Reinforced Concrete Panels", Ch. 3, p. 8, Ch. 1, p. 1. Manual fo Concrete Practice, ACI Committee 544 (1986), "State-of-the-Art Report on Fiber Reinforced Concrete", pp. 544.1R-1-22. Swedish Cement and Concrete Research Institute, Gram, H-E (1983), "Durability of natural fibres in concrete", pp. 98-131, 174-181. American Concrete Institute, An International Symposium: Fiber Reinforced Concrete (1974), article entitled "Some Properties of Glass Fiber Reinforced Concrete", pp. 93-111. Americna Concrete Institute, An International Symposium: Fiber Reinforced Concrete (1974), article entitled "Glass Fiber Reinforced Cement Base Materials", pp. 248-264. American Concrete Institute, an International Symposium: Fiber Reinforced Concrete (1974), article entitled "Glass Fiber Reinforned Cement Base Materials", pp. 350-362. Taylor, W.H. (1965), "Concrete Technology and Practice", pp. 178-180, Ch. 10, p.1.
Patent History
Patent number: 5690729
Type: Grant
Filed: Jan 27, 1995
Date of Patent: Nov 25, 1997
Assignee: Materials Technology, Limited (Reno, NV)
Inventor: Roger H. Jones, Jr. (Reno, NV)
Primary Examiner: Paul Macantoni
Law Firm: Townsend and Townsend and Crew
Application Number: 8/390,468